This invention relates to an information recording and reproducing apparatus for recording and reproducing information on and from a recording medium having a sector structure.
In an optical recording disk, optically detectable guide tracks such as guide grooves are provided concentrically or spirally in order to, for example, increase the recording track density and permit discrete, partial writing and erasure of information. A laser beam focused into a diameter less than or equal to 1 .mu.m is directed onto a recording layer formed on the guide tracks to record information by pitting or changing the reflection factor or transmission factor.
To deal with recording of digital information where the length of data is variable, the guide track is divided into a plurality of sectors for recording and reproducing the digital information on and from each sector. An example of a format of sector structure is shown in FIG. 11. It will be seen in FIG. 11 that each of the sectors is composed of a sector identifier 1 including track address and sector address information and a data field 2 for recording information thereon and reproducing information therefrom.
The data field 2 is generally composed of a pull-in signal part for pulling in a PLL (phase locked loop), a data head identification mark (abbreviated hereinafter as a data mark) added before recorded data for identifying the head of the recorded data, and a data part. At the time of demodulation of data, the data mark is detected from a reproduced signal for attaining word synchronization for the purpose of data demodulation.
On the other hand, when various defects, dust, scars or the like are present in the base material, recording film, protective layer, etc., of the optical recording disk, dropouts occur in the reproduced signal. Since the diameter of the recording pits and the pitch of the tracks on the optical recording disk are very small or in the order of about 1 .mu.m, a raw error rate is very bad or in the order of 10.sup.-4 to 10.sup.-5, and there are also many long burst-like dropouts. The operation of the PLL is frequently adversely affected by such burst-like dropouts. As a result, the word synchronization may become out of order at the time of demodulation of the data, and errors may occur on all the succeeding sector data.
With a view to solve such a problem, the inventors proposed in Japanese Patent Application No. 58-58157 to employ a sector format paving a frame structure in which each sector is divided into a plurality of information record units called frames hereinafter. Such a format will be explained with reference to FIG. 12. Referring to FIG. 12, data recorded in one sector is composed of data marks 3, m frames F.sub.1 to F.sub.m each containing a data unit 4 obtained by dividing one-sector data by m, and a pull-in signal part 5 affixed to the head of the first frame F.sub.1 for pulling in the PLL. Such a format is advantageous in that, even when the word synchronization becomes out of order at the time of data demodulation due to the presence of, for example, a long burst-like dropout as described above, the error is limited to only one frame unit, and normal demodulation can be carried out from the next frame.
As a data mark pattern, it is customary to utilize a special pattern different from that used in the conversion rule of modulation. For example, in the case of an MFM (modified frequency modulation) method, a modulation pattern such as a sequence of 2T, 1.5T and 2T (where T is the data rate) is not present and can therefore be easily discriminated from a row of modulated data.
FIG. 13 shows a flow of data in an optical information recording and reproducing apparatus. On write operation, user data supplied from a host 6 are temporarily stored in a data buffer memory 7, and after addition of an error correction code in an error detection and correction circuit 8, the data corresponding to one sector are stored in a sector buffer memory 9. The data are then modulated and formated in a modulation circuit 10, and the sector formated data are recorded on an optical recording disk by an optical disk drive 11. During a read operation, the reproduced signal from the optical disk drive 11 is demodulated in a demodulation circuit 12, and the demodulated sector data are stored in the sector buffer memory 9. After error correction processing in the error detection and correction circuit 8, the data are transferred to the host 6 through the data buffer memory 7.
However, when a data mark in the sector format of frame structure cannot be detected at the time of data demodulation due to the presence of, for example, a dropout, the data in that frame are not stored in the sector buffer memory 9. In such a case, the demodulated data in the succeeding frames will be stored at the successively-dislocated discrepant addresses, resulting in the storage of false data. Such a situation will be explained with reference to FIG. 14. It is supposed that the data corresponding to the frames F.sub.1, F.sub.2, F.sub.3, F.sub.4 and F.sub.5 are stored in the sector buffer memory 9 as shown in FIG. 14(a), and, after modulation in the modulation circuit 10 shown in FIG. 13, the modulated data are recorded on an optical recording disk by the optical disk drive 11 shown in FIG. 13. It is supposed then that the data mark of the second frame F.sub.2 is not detected at the time of data demodulation. In such a case, the data contained in and demodulated from the frame F.sub.2 are not stored in the sector buffer memory 9 as reproduced data, as shown in FIG. 14(b). Also, the data in the frame F.sub.3 are stored at the address at which the data in the frame F.sub.2 are to be primarily stored. Similarly, the data in the frame F.sub.4 are stored at the address at which the data in the frame F.sub.3 are to be primarily stored, and the data in the frame F.sub.5 are stored at the address at which the data in the frame F.sub.4 are to be primarily stored. In the manner above described, the data in one frame are stored at an address at which the data in the next frame are to be stored. Thus, all the data in the frames starting from the frame F.sub.2 are not stored at their assigned addresses.